During the process of welding a metal, it is common for the metal to become discoloured by the welding process. For example, when welding stainless steel, the chromium content of the metal is depleted, exposing iron and causing a localised discolouration of the stainless steel, known as “heat tint”. In other applications, oxides form during the welding process, leaving unattractive deposits on the surface of the metal, or otherwise discolouring the metal.
It is common practice that after a metal has been welded, the discoloured surfaces are cleaned to remove or reduce the heat tint. In the past, this has typically been performed by a variety of methods, such as using an abrasive, bead blasting or exposing the discoloured region to strong acids.
More recently, cleaning of welded joints has been performed using an electrically charged brush having conductive filaments, in conjunction with an electrolyte, to clean a metal surface by applying a concurrent chemical reaction, heat and electric current. The simultaneous electrolytic and high temperature cleaning action has proven successful in efficient cleaning of welded metals, particularly in cleaning stainless steel.
Known electrically charged brushes having conductive filaments can, however, suffer from a number of drawbacks. For example, known brushes can perform poorly because their relatively long filaments tend to flop on their sides, particularly when wet with electrolyte, rather than presenting erect filament ends as the working contact point. Applying the electrolyte to a weld with the filaments can therefore be somewhat haphazard, which is problematic because the electrolyte is typically highly acidic and spillage likely to cause damage.
The conductive brush for cleaning welded stainless steel disclosed in international PCT publication WO 2010/085849 was developed to address such a drawback. The brush disclosed in this patent application has a body connected to a fixed length of conductive brush filaments and a sheath arranged around the filaments. The sheath has an aperture through which the filaments extend having a profile of a particular geometry to shape the filaments retained within the sheath. The sheath is also movable with respect to the body and filaments, the movement adjusting the portion of brush filaments that protrude from the aperture, thereby adjusting the effective length and stiffness of the filaments.
Whilst the brush disclosed in WO 2010/085849 has various advantages over earlier brushes (e.g. as noted above), it also has a number of drawbacks. For example, the position of the sheath with respect to the filaments or body is freely adjustable and is unable to be locked. During use, this requires a user to manually maintain the position of the sheath or else the sheath may move from the desired position (e.g. when accidentally knocked whilst cleaning a weld, as can often happen), thereby adjusting the effective length and stiffness of the filaments. Such a requirement typically necessitates a two handed operation which, in addition to the cleaning manipulations, can make the brush very unergonornic to handle.
A need exists for a conductive brush assembly which overcomes, or at least ameliorates, one or more of the disadvantages of the prior art arrangements.